This invention relates to testing rotational torque producing devices and in particular to a method and apparatus for dynamically testing a rotational torque device under conditions simulating actual operating conditions.
A heat exchanger in a nuclear steam supply system extracts heat from a closed primary loop fluid that circulates through the reactor and the heat exchanger and transfers that heat to a closed secondary loop fluid that circulates through the heat exchanger and a steam turbine. The heat exchanger is comprised of a vessel containing a plurality of tubes around which the fluid of the primary loop passes and through which the fluid of the secondary loop circulates. Although the two fluids are in heat exchange relationship, it is imperative to maintain the fluids of the two loops isolated one from the other. Over the life of the nuclear steam supply system, some of the tubes of the heat exchanger deteriorate. During outages, the tubes of the heat exchanger are nondestructively tested to ascertain which tubes, if any, should be removed from service to assure the integrity of the heat exchanger.
One method of removing a heat exchanger tube from service is to plug both ends of the tube. One method of plugging a tube includes inserting a plug having an outside diameter less than the inside diameter of the tube being plugged. The plug is expanded by rolling the inner surface of the plug forming a mechanical rolled joint. The plug may be rolled either manually or automatically by use of remote installation equipment.
The rolling equipment is designed to stall at a predetermined torque. The integrity of the mechanical rolled joint is inferred from the torque at which the rolling equipment stalls. The rolling equipment is calibrated periodically to ensure a consistent, acceptable rolled joint.
Commercial equipment designed to calibrate rolling equipment to assure that the stall torque remains within an acceptable tolerance band either operates by running the torque producing device up to an operating speed and having a sudden stop or by coupling the torque producing device directly to a rigid torque measuring device and energizing the torque producing device. Neither of the commercial torque measuring devices provide acceptable calibration of the torque producing device for expanding plugs to form a mechanical rolled joint. In running the torque producing device up to speed then suddenly stopping the torque producing device, any measured torque is comprised of both the torque produced by the device and the rotational inertia of the torque producing device. Starting a torque producing device against an infinite load while monitoring the torque produced does not provide an indication of the stall torque but rather an indication of the starting torque of the torque producing device.
A method and apparatus for testing the stall torque produced by a torque producing device under conditions which are similar to actual operating conditions is needed. Such a method and apparatus would permit calibration of rotational torque producing devices such that when a calibrated torque producing device is used to produce a mechanical rolled joint the integrity of the mechanical rolled joint may be consistently and reliably inferred from the calibration of the rotational torque device.